This Section has focused on the role of Ca++ as a regulator of gene expression and cellularphysiology. Using CAI as a tool, we have investigated Ca++-regulated molecular events. A novel gene, CAIR-1, was cloned from CAI conditioned cells. Studies over the past year have investigated the signal transduction function of CAIR-1 and were initiated to identify a function for CAIR-1. We have demonstrated by cellular fractionation and immunohistochemistry that CAIR-1 is a cytosolic protein that is found broadly within the cell by confocal immunofluorescence. CAIR-1 is expressed in vascular tissue and epithelial cells of multiple tumor types with no clear difference yet defined between tumor and normal cells; there is minimal expression in stroma. It is present in the epithelial cells of ovarian carcinoma specimens and stains their small vessels as well. A borderline ovarian cancer specimen also showed limited staining for CAIR-1. Staining was also seen in kidney cancer, breast cancer, and colon cancer specimens. Cohorts are now being assembled to determine if CAIR-1 expression by cellular localization or relative quantity may be a marker for malignancy or aggressiveness. Pre- and post- CAI treatment specimens will be obtained in the current phase II CAI clinical trial and will be tested for changes in CAIR-1 expression by immunohistochemistry and/or RT-PCR. CAIR-1 function studies are being driven by putative functional domains in the protein. The PXXP regions suggest that CAIR-1 should bind SH3-containing proteins. Our hypothesis that CAIR-1 should function downstream of a calcium-regulated or calcium-associated pathways led to the identification of phospholipase C-gamma (PLC-g) as a putative partner protein. Coimmunoprecipitation studies indicate that CAIR-1 binds to PLC-g under basal conditions and is dissociated when cells are stimulated with epidermal growth factor. Transfection studies have begun directed at expression of full length CAIR-1 and its putative domains, as potential dominant negative constructs. These transfectants will be analyzed for functional status and alterations in calcium related signal transduction. - signal transduction, calcium, phospholipase C,